Shared ground
This passage treats “Scripture” as carrying a God-given quality (“inspired by God”) and, because of that, as useful in concrete ways. The usefulness is not only about giving information; it has a shaping function: it teaches, exposes what is wrong, corrects what has gone off course, and trains people in a way of life aligned with what is right.
The stated goal is formation. Scripture’s work is aimed at making “the man of God” complete and fully outfitted for “every good work.” Explicitly, the text links Scripture’s source to Scripture’s practical effect.
Where interpretation differs
What “every Scripture” refers to. Some read the phrase as focusing on each individual passage (“each Scripture is God-breathed and useful”). Others read it as a collective statement about Scripture as a whole (“all Scripture is God-breathed and useful”). Either way, the point remains broad: Scripture is characterized by a divine origin and real usefulness.
Which writings are in view. In the letter’s setting, “Scripture” naturally points to the sacred writings Timothy already knew (3:15), which would primarily be Israel’s Scriptures. Many also infer that the principle extends to later Christian writings recognized as Scripture, but that extension is an inference beyond what these two verses explicitly list.
Who “the man of God” is. Some take it mainly as a description of a recognized leader (especially a teacher), since the surrounding context focuses on sound teaching and ministry. Others take it more broadly as any person devoted to God. The difference affects how narrowly or widely the stated purpose (“equipped for every good work”) is applied.
Why the disagreement exists
The Greek wording can be read in more than one natural way (whether “every” highlights individual parts or the whole). Also, “Scripture” is a shared label, but what counts as Scripture is partly a question of historical scope—what the author and Timothy would have had in hand at the time versus what later communities came to include.
What this passage clearly contributes
It explicitly claims that Scripture is “inspired by God” and that it is “profitable” for four listed functions: teaching, reproof, correction, and training in righteousness. It also explicitly gives a purpose statement: Scripture is meant to produce a certain kind of readiness—completeness and full equipment for every kind of good work. The passage therefore frames Scripture as both authoritative in origin and practical in outcome, especially in contexts threatened by distorted teaching and unstable character (3:13–4:5).